As winter approaches people are asking how to get more heat out of those very old hot water radiators. A few tips.
Bleed the air out anytime they don't feel hot enough. This will usually be only one or two that have problems while the rest are hot. If they all are cold you may need to check the boiler or the circulation pump. You can get automatic bleeder valves that will let any bubbles out as the bubbles show up. They can cause slight dripping with age, so you can even get bleeder valves that have drip hoses attached for fool proof automatic bleeding. Best of all there is a fully automatic air purging system that permenantly removes all water from the system, check out SpiroVent. You will have to drain the system to install these so make this improvement in the summer time.
If the rad is not hot enough, check that the valve is all the way open. It is occasionally a good idea to close it all the way and then open it all the way, just to get its parts moving. If it wants to leak at the stem after playing with it, simply tighten the packing nut under the handle. In most hot water systems, this valve can be used to turn a hot radiator down a bit cooler.
Scrap into the paint with a knife. If there are three coats of paint or more, it is time to strip it. Paint is an insulator and greatly reduces the heat output of radiators. Replace it with metallic paint.
Wrap household aluminium foil around a piece of cardboard and put it behind the radiator. That will radiate back the heat that would normally go into the wall, and greatly increase the heat output of a radiator. The aluminium has to be clean for this to work, so don't use any expensive aluminium, like the bubble wrap stuff. Just use household aluminium and replace it occasionally -- shiny side towards the radiator.
If your house has no central air circulation, but does have high ceilings, installing the large-blade ceiling fans will increase comfort by redistributing the hot air off the ceiling (although not save any real energy).
Central exhaust fan systems help move air around, but do not improve the heating in the house. Central iar change systems can use radiators to pre-heat the incoming air and this does increase the comfort of the house (fewer cold air drafts).